Mechanical parts for the turbines revolving at a high speed under a high-temperature, high-humidity condition and the apparatuses and devices driven in an extreme environment such as the driving devices in space station should be made of a material lower in friction, and such environments cause problems of oxidation of the parts due to exposure to the high-temperature high-humidity condition and increase of the friction coefficient of the parts due to collision of atomic oxygen to the parts (oxidative degradation).
Use of an oxide-based low-friction material may be a possible way to overcome the problems above, but there is actually, almost no such oxide material available.
For example, copper oxide, which is prepared from a cheap raw material and easier in handling, has a high friction coefficient of approximately 0.2 or more in the atmosphere and in vacuum even if it is formed by surface oxidation, and thus, it is considered to be difficult to use it as a low-friction material. Actually, the friction coefficients thereof so far reported are larger at 1.6 in the atmosphere and 0.4 in vacuum (J. R. Whitehead, Proc. Roy. Soc A210 (1850) 109).
However, a low-friction oxide thin film material, if made available, can be prepared from an extremely cheap raw material and is free from the concern about the increase in friction coefficient due to oxidation because it is already oxidized, and thus would be used favorably in various fields including the power generation and aerospace fields.
An object of the invention of the present application, which was made under the circumstances above, is to provide a new technical means of facilitating formation of a thin film having a low friction coefficient.